Conventionally, there are demands for a reduction in power consumption in a display device such as a liquid crystal display device. In recent years, hence, developments have been made in a driving method involving “providing a pausing period between a writing period and a writing period in order to pause a write operation by bringing all gate bus lines (scanning signal lines) into a non-scanning state” for a liquid crystal display device. It should be noted that the writing period refers to a period for charging a pixel capacitance in a display unit, based on an image signal in one frame (one screen). The writing period is also called, for example, a scanning period, a charging period, or a refreshing period. According to the driving method described above, there is no need to apply, for example, a controlling signal to a liquid crystal drive circuit (e.g., a gate driver, a source driver) in the pausing period. Therefore, a drive frequency of the liquid crystal drive circuit is reduced as a whole, so that a reduction in power consumption can be realized. It should be noted that the driving method involving providing the pausing period for pausing the write operation is called, for example, “low-frequency driving” or “pause driving”. FIG. 3 is a diagram for illustrating one example of the low-frequency driving. In a liquid crystal display device that employs the low-frequency driving, as shown in FIG. 3, for example, a writing period having a length corresponding to a one frame period (one frame period: 16.67 ms) in a general liquid crystal display device having a refresh rate (a drive frequency) of 60 Hz and a pausing period having a length corresponding to a 59-frame period appear alternately. This low-frequency driving is suitable for still image display.
In recent years, attention has been given to a thin-film transistor using an oxide semiconductor as a channel layer (hereinafter, such a thin-film transistor is referred to as an “oxide TFT”). The oxide TFT has an off-leak current (i.e., a current to be flown in an OFF state) which is considerably smaller than that of a thin-film transistor using, for example, amorphous silicon as a channel layer (hereinafter, such a thin-film transistor is referred to as a “silicon-based TFT”). Therefore, a liquid crystal display device using an oxide TFT as an element in a liquid crystal panel is capable of holding a voltage written on a pixel capacitance, for a relatively long period of time. Accordingly, the low-frequency driving described above is particularly employed for a liquid crystal display device using the oxide TFT as an element in a liquid crystal panel. The low-frequency driving is occasionally employed for a liquid crystal display device using the silicon-based TFT as an element in a liquid crystal panel.
A liquid crystal has a characteristic in that the liquid crystal is degraded when being successively applied with a direct-current voltage. Accordingly, in a liquid crystal display device, a liquid crystal is driven such that the polarity of a voltage (pixel voltage) on a pixel electrode, in a case where a voltage (common electrode voltage) on a common electrode is defined as a reference, is reversed every predetermined period. Assuming that such reversal driving is performed, the common electrode voltage is subjected to an adjustment such that a charging rate at the time when a write operation with positive polarity is performed (at the time when the polarity of the pixel voltage is positive) becomes equal to a charging rate at the time when a write operation with negative polarity is performed (at the time when the polarity of the pixel voltage is negative). This adjustment is called, for example, a “counter adjustment”. Moreover, the common electrode voltage to be adjusted such that the charging rate at the time when the write operation with positive polarity is performed becomes equal to the charging rate at the time when the write operation with negative polarity is performed is called, for example, an “optimum counter voltage”. Generally, the counter adjustment is made such that flicker is not visually recognized at a certain point on a display unit. Typically, the counter adjustment is made such that flicker is not visually recognized at a center portion of a display unit. The degradation in liquid crystal is effectively suppressed in such a manner that the reversal driving is performed after the counter adjustment.
It should be noted that, in relation to this invention, Japanese Patent Application Laid-Open No. 2008-164852 discloses a liquid crystal display device having the following configuration. An image area is divided into four areas, and common electrode voltages which are different in magnitude from one another can be applied to these four areas. In this liquid crystal display device, the occurrence of flicker is suppressed by setting the value of the common electrode voltage at an optimum value for each area (i.e., by performing counter adjustment for each area).